Cosmic car crash!

You are riding with Mom in your family's big sport utility vehicle. You are on the freeway, going 65 miles per hour. Suddenly, a mini-car up ahead moves over into your lane. But the mini-car is going only 40 miles per hour! Mom tries to slow down, but it's too late. Your SUV crashes into the rear of the little car! Fortunately, another driver in a passing car saw the whole thing and even took pictures!

Now, imagine the SUV is a comet and the mini-car is a tiny spacecraft. This is NASA's Deep Impact mission.

After being launched in January 2005, Deep Impact met up with Comet Tempel 1 on July 3, 2005. Just 24 hours before this meeting, a part of the spacecraft, called the smart impactor, separated from the other part, called the flyby spacecraft. The impactor flew all by itself right smack into the path of the comet! The comet was traveling a lot faster, so BLAM! The impactor crashed into the comet . . . or rather, the comet crashed into the impactor at 36,000 kilometers per hour (or 23,000 miles per hour)! Whoever crashed into whom, the impact caused a big flash of light, threw up a lot of debris, and left a big crater!

The point of this "planned accident" is to do a space experiment and find out what's inside the comet. That's where the "flyby" part of the spacecraft comes in. The flyby spacecraft has telescopes and a spectrometer. It used these to take pictures of the impact and analyze the material blasted into space from inside the comet.

Before Deep Impact, nobody knew exactly what the inside of a comet was like. Like a chocolate candy, a comet may look dark and crusty on the outside, but be filled with something very different in the center (creamy nougat? chewy carmel? hard toffee? nuts?). Now scientists have lots of pictures and other information to study. Scientists want to find out all about comets, because comets are the icy leftovers from the birth of our solar system. Understanding more about them will help fill in the gaps in our knowledge of how the solar system formed.